Filter cartridges for air filtering devices are usually used as filter elements of a filtering face mask that comprises a mask body adapted to fit over the nose and mouth of a person such that the air the person breathes passes through the filter cartridge and is cleared from harmful components such as fine dust, dust or other components. For comfort and design reasons it is desirable to obtain a filter cartridge having the shape adapted to the general shape of a person's face. In particular, it is desirable to have a cartridge that is curved to at least one direction. While manufacturing a housing of a curved cartridge is not a problem, providing a curved filter bed is, since conventional storm filling techniques are not sufficient for a curved filter bed.
Corresponding attempts have been made for example in the European patent specification EP 0 309 277 B1 where a method of manufacturing a filtering device involves the use of an injection mold that is adapted to receive a resilient, porous, substantially rigid filtration element and resin injected into the mold at a certain pressure to form a solid, molded filtering device that may have a curved shape. The mold process as such, however, is cost-intensive and time-consuming.
The international publication WO 2009/145992 A1 discloses another air filtering device having a curved filter bed of a loose filter material. The filter material is held by a cartridge that comprises a cup-shaped casing and a discoidal lid. During manufacturing the filter material is deposited on the flat horizontally oriented support plate in particular by storm filling. Afterwards, the support plates are deformed to obtain a filter bed having at least one curvature. This requires the casing or the lid to be flexible in nature and some kind of support structure that keeps the cartridge of the filter bed in its curved shape.